Economical and environmental concerns, e.g., improving efficiency and reducing emissions, are driving forces behind the ever increasing demand for higher gas turbine inlet temperatures. A limitation to the efficiency and emissions of many gas turbine engines is the temperature capability of hot section components such as blades, vanes, blade tracks, and combustor liners. Technology improvements in cooling, materials, and coatings are required to achieve higher inlet temperatures. As the temperature capability of Ni-based superalloys has approached their intrinsic limit, further improvements in their temperature capability have become increasingly difficult. Therefore, the emphasis in gas turbine materials development has shifted to thermal barrier coatings (TBC) and next generation, high temperature materials, such as ceramic-based materials.
Silicon carbide/silicon carbide (SiC/SiC) ceramic matrix composite (CMC) materials are prime candidates to replace Ni-based superalloys for hot section structural components for next generation gas turbine engines. The key benefit of SiC/SiC CMC engine components is their excellent high temperature mechanical, physical, and chemical properties which allow gas turbine engines to operate at much higher temperatures than the current engines having superalloy components. SiC/SiC CMCs also provide the additional benefit of damage tolerance, which monolithic ceramics do not possess.
The present disclosure is related to environmental barrier coatings that extend the life of components in a turbine environment.
An illustrative embodiment of the present disclosure provides a fiber having an environmental barrier coating, comprising: a Hi Nicalon preform assembled in a tooling for chemical vapor infiltration and cleaned to remove sizing char from fibers of the Hi Nicalon preform; a ytterbium doped silicon carbide coat located over the Hi Nicalon preform; a boron nitride interface coat applied over the ytterbium doped silicon carbide coat; and a silicon carbide coat applied over the boron nitride interface coat.
In the above and other illustrative embodiments the fiber having the environmental barrier coating may further comprise: the boron nitride interface coat has a thickness of about 0.5 μm; the silicon carbide coat has a thickness of about 2 μm; the Hi Nicalon preform includes about 36% fiber volume and cleaned using air at about 600 degrees C.; the preform being completed with slurry and melt infiltration; the ytterbium doped silicon carbide coat being applied by chemical vapor infiltration; and the silicon carbide coat being applied by chemical vapor infiltration.
Another illustrative embodiment of the present disclosure provides a fiber having an environmental barrier coating, comprising: a Hi Nicalon S fiber; the Hi Nicalon S fiber is coated in tow form with yttrium doped silicon carbide; and a silicon doped boron nitride coat applied over the yttrium doped silicon carbide.
In the above and other illustrative embodiments the fiber having the environmental barrier coating may further comprise: the Hi Nicalon S fiber being coated with about 1 μm of the yttrium doped silicon carbide; the silicon doped boron nitride coat having a thickness of about 0.3 μm; the fiber being coated with silicon nitride of about 0.3 μm and silicon carbide of about 0.1 μm; the tow is processed with a silicon carbide slurry and binders to form a unidirectional tape; the uni-directional tape is laminated and shaped, then cured; a resulting body being infiltrated with silicon to complete a CMC component; the yttrium doped silicon carbide being applied by a chemical vapor deposition process; and the silicon doped boron nitride coat being applied by the chemical vapor deposition process.
Another illustrative embodiment of the present disclosure provides a fiber having an environmental barrier coating, comprising: a T-300 carbon fiber preform assembled in tooling for chemical vapor infiltration; alternating layers of silicon carbide and boron carbide are applied over the preform; and a silicon doped boron nitride interface coat applied over the silicon carbide coat.
In the above and other illustrative embodiments the fiber having the environmental barrier coating may further comprise: the T-300 carbon fiber preform includes about 36% fiber volume, the silicon carbide coat and boron carbide coat each have a thickness of about 0.1 μm each for a total of 0.7 μm; and wherein the silicon doped boron nitride interface coat has a thickness of about 0.5 μm; the matrix densification continues by chemical vapor infiltration with alternating layers of silicon carbide and boron carbide at about a nominal thickness of about 0.1 μm until full density is achieved; and the alternating layers of silicon carbide and boron carbide include four layers of silicon carbide and three layers of boron carbide.
It should be appreciated that the present application discloses one or more of the features recited in the appended claims and/or the following features which alone or in any combination may comprise patentable subject matter.